1. Field of the Invention
The present invention relates to a pressure gauge which is provided part way along a pipeline, and measures the pressure of a fluid flowing through the pipeline.
2. Background Art
As shown in FIG. 7, in those cases where the pressure of a fluid flowing through a pipeline 1 is to be measured, typically a pressure gauge 2 is provided part way along the pipeline 1.
This pressure gauge 2 is attached by screwing the gauge into a mounting aperture 5 provided within a joint 4 connecting the pipeline 1, and detects the pressure of fluid flowing through a fluid passage 6 which is formed inside the joint 4 and interconnects the two sections of the pipeline 1. The pressure of the fluid is then displayed via a display section 8 comprising a display needle 7.
As shown in FIG. 8, this pressure gauge 2 comprises a mounting section 11 on which is formed the male screw thread for screwing into the mounting aperture 5 of the joint 4, and a measurement section 12 which is fixed to the mounting section 11.
A pressure detection aperture 11a is formed in the mounting section 11, and the fluid pressure from this pressure detection aperture 11a acts upon a diaphragm 13.
This diaphragm 13 is shaped as a circular cylinder with a closed base, and the outer surface of the diaphragm 13 forms a concertina shaped compressible bellows section 14. An actuator rod 15 of the measurement section 12 is inserted through the top of the diaphragm 13.
In this type of pressure gauge 2, the compressible diaphragm 13 is provided so that the fluid never contacts the actuator rod 15 of the measurement section 12 directly, but rather the fluid pressure is transmitted to the actuator rod 15 via the diaphragm 13.
When the pressure of the fluid flowing through the pipeline 1 is transmitted from the pressure detection aperture 11a of the mounting section 11 to the diaphragm 13, the diaphragm 13 is compressed upwards under the pressure of the fluid, and the actuator rod 15 inserted inside the diaphragm 13 is lifted up, and accompanying this upwards movement of the actuator rod 15, the display needle 7 of the display section 8 of the measurement section 12 rotates to display the pressure.
However, in the aforementioned pressure gauge 2, in those cases in which highly corrosive chemicals flow through the pipeline 1, those sections which come in contact with the fluid are formed from polytetrafluoroethylene resin, which is a highly chemical resistant material, although the bellows section 14 of the diaphragm 13 needs to be of a very thin construction in order to ensure good compressibility. As a result, gas permeation occurs through the bellows section 14 of the diaphragm 13, and so the metallic actuator rod 15 inserted inside the diaphragm 13, together with other metallic material sections within the measurement section 12 are subjected to corrosion, causing measurement errors and reducing the lifespan of the gauge.
The present invention takes the above issues into consideration, with an object of providing a pressure gauge with excellent chemical resistance, which is capable of accurately measuring fluid pressure, even if the fluid is a highly corrosive chemical.
In order to achieve the above object, a pressure gauge of the present invention comprises a mounting section which is connected to a pipeline, and a measurement section which is provided on the mounting section, and in which the upwards movement of an actuator rod causes a rotation of a display needle. In the mounting section, a concave section is provided in which the bottom thereof interconnects with the inside of the pipeline, and inside this concave section is provided a diaphragm which is shaped as a circular cylinder with a closed base, with an outer surface comprising a compressible bellows section formed as a concertina shape in an axial direction, and with a central aperture which functions as a housing aperture for housing the tip of the actuator rod, and the pressure of fluid within the pipeline acts upon the base of the diaphragm, compressing the diaphragm. At the tip of the actuator rod housed within the housing aperture is installed a corrosion resistant protective cap which covers this tip section.
Because a protective cap covers the tip section of the actuator rod housed inside the housing aperture of the diaphragm, even if a corrosive fluid undergoes gas permeation through the bellows section of the diaphragm, any direct contact with the actuator rod is prevented, and as a result, measurement errors and any reduction in the lifespan of the gauge resulting from corrosion of the actuator rod can be prevented.
In the above pressure gauge, a flexible, corrosion resistant seal may also be provided between the mounting section and the measurement section for partitioning the two sections, and the aforementioned actuator rod can be inserted through the center of the seal, with the seal being held in place between a fixed flange formed in the central region of the actuator rod and the protective cap.
In those cases in which the mounting section and the measurement section are partitioned with a flexible, corrosion resistant seal in this manner, any gaseous fluid which permeates the bellows section of the diaphragm on the mounting section can be prevented from reaching the measurement section, without hindering the movement of the actuator rod, and measurement errors and any reduction in the lifespan of the gauge resulting from corrosion of the measurement section can be prevented with even greater certainty.
The seal around the periphery of the actuator rod may also comprise a slack section which displays a degree of slack in a radial direction.
In such a case, because the seal around the periphery of the actuator rod comprises a slack section which displays a degree of slack in a radial direction, any obstruction of the movement of the actuator rod resulting from the provision of the seal can be almost completely prevented.
The top and bottom of the seal around the periphery of the actuator rod may also comprise hollow sections which link through to the open air.
In such a case, because the hollow sections formed in the top and bottom of the seal link through to the open air, when the seal deforms as a result of following the movement of the actuator rod, any pressure variation between the top and bottom of the seal can be minimized, enabling any obstruction of the movement of the actuator rod resulting from the provision of the seal to be even more completely prevented.
An O ring may also be provided between the outer periphery of the diaphragm at the upper end of the bellows section, and the inner periphery of the concave section of the mounting section.
In such a case, the O ring provided between the outer periphery of the diaphragm at the upper end of the bellows section and the inner periphery of the concave section of the mounting section completely prevents any leakage of fluid through the gap between these two sections, thereby completely preventing any deleterious effects on the measurement section resulting from such leaked fluid.